This invention relates to optical radar of the type which illuminates targets by means of a laser beam and derives target information from the reflected laser beam. Such radars usually include a scanning and tracking capability. The scanning system moves the transmitted laser beam over the field of view, usually in some systematic manner, for example with a sawtooth scan system of the type used in television or with spiral type scanning. If such a radar is provided in addition with a tracking capability for moving targets, the scan format must be randomly programmable so that random target movements can be followed.
Scanner/trackers for laser beams may include a coarse scanner, for example a wide angle, low speed, low resolution scanner; with a narrow field, high resolution, high speed dither scanner in series with the coarse scanner. With such a dual mode scanner/tracker system, the coarse scanner may for example scan in a sawtooth fashion with gaps between the scanning lines, with the high speed dither scanner filling in the gaps. Thus the two scanners complement each other. In the tracking mode both of these scanner/trackers move in a programmed coordinated manner to achieve target tracking.
Scanners of this type usually achieve laser beam movement by means of moving optics such as rotating prisms or wedges through which the beam passes or electrically driven moving mirrors from which the beam is reflected. High speed tracking, such as is required for the aforementioned dither scanner/tracker requires extremely high power if the moving optics are located at a point where the laser beam has its largest diameter. Laser radars normally include a means to expand the beam diameter before transmission to improve angular resolution or provide greater range.